The bus, which belongs to the Nghe An Huu Nghi tourism company, was taking 36 people, some of them from the northern province of Son La, on a seven-day trip through Laos and Thailand for VND9.6 million (US$460) a person.

"I was sitting on the first range. I was about to fall asleep when the bus suddenly flipped over. There were many shouts and cries, and I fell unconscious," Tong Van Lot, 68, one of the passengers, told news website VietNamNet.

All the victims were couples between 50 and 77, except for the 32-year-old driver. They have yet to recall what caused the accident.

Ha Tanh, 71, from Son La said he only remembers "a miserable scene with blood everywhere and people crying desperately."